As a software developer I would like to refactor ApplyConstantInterpolateLinePressureProcess, which is created in FORTRAN-like style. This process does not have any unit tests only integration tests. Therefore, unit tests have to be added before the refactoring.

A few things TODO

• 'undefined ids' should really be avoided,
• the complexity shall be lower,
• it would be a good idea to just make sure everything in this class is in terms of std::size_t, since the Id() functions return this.

For ApplyWriteScalarProcess

• The Execute method of the base is also just an empty function, so I don't think we need to override it, we could just remove the function.

To be corrected:

• The text "No boundary node is found" does not tell a user where and how to fix the encountered problem. If possible we should tell for which modelpart and which process this appears.
• "There is not enough points around interpolation, node Id"

Think about:

• A side note is that the setup in Kratos of the processes running subsequently and each for themselves deciding whether they should free a D.o.F. makes the outcome dependent on the order of the processes.